Remotely read identification tags have a wide range of different applications and uses (see for example RFID HANDBOOK “Radio-Frequency Identification Fundamentals and Applications” by Klaus Finkenzeller, John Wiley & Sons Ltd, Baffins Lane, Chichester, West Sussex, P019 1UD, England, ISBN 0 471 98851 0). One of the technologies is the capacitively coupled identification system such as Motorola's BiStatix™ technology. In these systems the smart part of the tag is in a silicon based integrated circuit placed in proximity to the antenna unit (capacitive coupled antenna). This chip together with the capacitevely coupled antenna unit is used to transmit a signal, usually an identification code. The connection between the integrated circuit and the antenna plates (usually two) may be via a transistor inside the circuit. The signal from the integrated circuit is, via the transistor, used for modulating the antenna characteristics in such a fashion that the receiver can recognise the signal and detect an ID code.
Semi-conducting and conducting organic materials, both polymers and molecules, have successfully been included in a large range of electronic devices, e g electrochemical devices, for instance as dynamic colorants in smart windows and in polymer batteries. Reversible doping and de-doping involving mobile ions switches the material between different redox states.
Use has been made of semi-conducting polymers for the realisation of field effect transistor (FET) devices. The transistor channel of these devices comprises the semi-conducting polymer in question, and their function is based on changes in charge carrier characteristics in the semi-conducting polymer, caused by an externally applied electric field. In such transistors, the polymer is used as a traditional semiconductor, in that the electric field merely redistributes charges within the polymer material. One such transistor has been realised, which is adapted for miniaturisation and can be used for the production of integrated circuits consisting entirely of polymer material (PCT publication WO99/10939). A stack of sandwiched layers is described, with either a top-gate or a bottom-gate structure. A transistor device with a similar architecture, also using a polymer as semi-conducting material in the channel of the transistor, is described in the European patent application EP 1041653.
Another type of transistor device based on organic materials utilises electrochemical redox reactions in the organic material. These devices comprise an electrolyte and a conducting polymer that can be switched between an oxidised and a reduced state. One of these oxidation states then corresponds to low, preferably zero, conductivity in the material, whereas the other oxidation state corresponds to a high conductivity relative to the first state. Electrochemical transistor devices have been used as sensors, e g for detection of oxidant in a solution (see, for review, Baughman and Shacklette, Proceedings of the Sixth Europhysics Industrial Workshop (1990), p 47-61). Furthermore, a transistor of the electrochemical type is reported in Rani et al, J Solid State Electrochem (1998), vol 2, p 99-101. The gate electrode architecture in this prior art transistor is shown in FIG. 1 of this reference.
Problems with capacitively coupled identification devices in the prior art include that they are difficult and expensive (>0.50 USD) to manufacture. In particular, the chip part of the identification unit is limiting the capability to mass-produce the tags to lower prices. Furthermore, materials used in the chips of prior art devices suffer from a lack of environmental friendliness, processability and economic production possibilities. Consequently, there is a need for new and improved identification circuitry with a simplified antenna-logic connection.